All-solid lithium secondary battery

Abstract

An exemplary all-solid lithium secondary battery includes a positive electrode including a positive-electrode active substance layer, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode. The positive-electrode active substance layer is composed of lithium cobaltate, and has an α-NaFeO 2 type crystal structure. The positive-electrode active substance layer has a (018) plane oriented in a normal direction of a principal face of the positive-electrode active substance layer. The solid electrolyte layer is composed of lithium lanthanum titanate and has a tetragonal perovskite-type crystal structure. The solid electrolyte layer has a (110) plane or a (102) plane oriented in a normal direction of a principal face of the solid electrolyte layer.

What is claimed is: 
     
       1. An all-solid lithium secondary battery comprising:
 a positive electrode including a positive-electrode active substance layer; 
 a negative electrode including a negative-electrode active substance layer, the negative-electrode active substance layer allowing lithium ions to be inserted and allowing inserted lithium ions to be released; and 
 a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein, 
 the positive-electrode active substance layer comprises lithium cobaltate, and has an α-NaFeO 2  type crystal structure; 
 the positive-electrode active substance layer has a (018) plane oriented in a normal direction of a principal face of the positive-electrode active substance layer; 
 the solid electrolyte layer comprises lithium lanthanum titanate and has a tetragonal perovskite-type crystal structure; and 
 the solid electrolyte layer has a (110) plane or a (102) plane oriented in a normal direction of a principal face of the solid electrolyte layer. 
 
     
     
       2. The all-solid lithium secondary battery of  claim 1 , wherein the positive-electrode active substance layer and the solid electrolyte layer are epitaxial films. 
     
     
       3. The all-solid lithium secondary battery of  claim 2 , wherein the solid electrolyte layer is an epitaxial film that matches a crystal orientation of the positive-electrode active substance layer. 
     
     
       4. The all-solid lithium secondary battery of  claim 1 , wherein a [−4-81] direction in the positive-electrode active substance layer is parallel to a [001] direction or a [010] direction in the solid electrolyte layer, and a [100] direction in the positive-electrode active substance layer is parallel to a [1-10] direction or a [−201] direction in the solid electrolyte layer. 
     
     
       5. The all-solid lithium secondary battery of  claim 1 , wherein, in an X-ray diffraction pattern of the positive-electrode active substance layer, a ratio (I(018)/I(003)) between a peak intensity I(018) of the (018) plane and a peak intensity I(003) of the (003) plane satisfies the relationship I(018)/I(003)>20. 
     
     
       6. An all-solid lithium secondary battery comprising:
 a positive electrode including a positive-electrode active substance layer; 
 a negative electrode including a negative-electrode active substance layer, the negative-electrode active substance layer allowing lithium ions to be inserted and allowing inserted lithium ions to be released; 
 a solid electrolyte layer interposed between the positive electrode and the negative electrode, wherein, 
 the positive-electrode active substance layer comprises lithium cobaltate, and has an α-NaFeO 2  type crystal structure; 
 given an x axis and a y axis which are defined as two axes that are parallel to a principal face of the positive-electrode active substance layer, and a z axis which is defined as an axis that is perpendicular to the principal face, 
 the positive-electrode active substance layer is composed only of first regions having a (110) plane oriented in the z axis direction and second regions having a (018) plane oriented in the z axis direction, the first regions and second regions being mixedly present in an xy plane of the positive-electrode active substance layer; 
 the solid electrolyte layer comprises lithium lanthanum titanate and has a tetragonal perovskite-type crystal structure; and 
 the solid electrolyte layer has a (110) plane or a (102) plane in a normal direction of a principal face of the solid electrolyte layer. 
 
     
     
       7. The all-solid lithium secondary battery of  claim 6 , wherein the positive-electrode active substance layer and the solid electrolyte layer are epitaxial films. 
     
     
       8. The all-solid lithium secondary battery of  claim 7 , wherein the solid electrolyte layer is an epitaxial film that matches a crystal orientation of the positive-electrode active substance layer. 
     
     
       9. The all-solid lithium secondary battery of  claim 6 , wherein, in an X-ray diffraction pattern of the positive-electrode active substance layer, a ratio (I(110)/I(018)) between a peak intensity I(110) of the (110) plane and a peak intensity I(018) of the (018) plane is 0.3 or 1.0. 
     
     
       10. The all-solid lithium secondary battery of  claim 2 , wherein the positive-electrode active substance layer is formed on a current collector which is a strontium titanate substrate, the strontium titanate substrate being doped with a dopant and electrically conductive. 
     
     
       11. The all-solid lithium secondary battery of  claim 7 , wherein the positive-electrode active substance layer is formed on a current collector which is a strontium titanate substrate, the strontium titanate substrate being doped with a dopant and electrically conductive.